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Does surface roughness really matter in nanowires?

Oct 9, 2013
2013-10-09T09:00:00+0100

New experiments by researchers at the City University of Hong Kong have revealed that surface roughness can degrade electron mobility in miniaturized and surface-disordered nanowires. These findings mean that nanowire geometries and surface properties should be taken into account when designing high-performance devices.

III-V semiconducting nanowires (NWs) such as indium arsenide (InAs) have been extensively studied as fundamental building blocks for transistors, optoelectronics and other electronics devices, thanks to the extraordinary carrier mobility of these materials. Until now, however, few experiments have directly addressed the effects of surface roughness on the electronic transport properties of NWs – something that is critical for high-performance electronic devices.

A team led by Dr Johnny Ho and Professor K S Chan synthesized InAs NWs with controllable diameters and surface roughness using a catalytic chemical-vapour-deposition technique. Combined with detailed atomic force microscopy (AFM) and electrical characterization of devices made from the NWs, the researchers found that electron mobility monotonically degrades with increasing surface roughness and diameter scaling (from around –6000 cm2 V–1 s–1 nm–1 to around 300–500 cm2 V–1 s–1 nm–1). Cryogenic measurements further decoupled the effects of surface/interface traps and phonon scattering, highlighting the significance of surface scattering in the miniaturized NWs. Smaller NWs have a larger surface-area-to-volume ratio, which means that their surface properties are more important.

The mobility values of rough NWs were also found to be less sensitive to changes in diameter than smooth NWs – which is due to the stronger effective scattering potential. When roughness occupies a larger fraction of the NW cross-section, the modulation in the scattering potential induced by the diameter change is less effective. This means that reduction in mobility from the decrease in diameter is smaller in a rough NW.

Although InAs NWs were studied in this work, the findings could also be extended to other NW material systems.

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About the author

Johnny C Ho, PhD is an assistant professor in the Department of Physics and Materials Science at the City University of Hong Kong. His research group is currently investigating the synthesis, characterization and device integration of nanostructured materials for various technological applications in electronics, photonics and sensors. This article first appeared at nanotechweb.org